As batteries play a larger role in powering the movement of vehicles such as cars, systems that employ a plurality of batteries have been designed. Different batteries will have different capacities, different self-discharge rates and/or different impedances that will affect the performance of these systems. For instance, drawing a high current from these systems can cause the voltage of one or more batteries to fall to a dangerously low level and fail while the remaining batteries remain operational. The failure of the battery can cause failure of the entire system. Because prior systems have not adequately addressed the variations in the performance of different batteries there is a need for an improved battery system.